The invention is relative to a device for regulating the tension of a running belt and to a method for regulating the tension of a running belt.
Rotating screen belts for dewatering paper webs are known from practice. The paper web is pressed against the screen belt in order to press water out of the paper web. The rotating belt is deigned as an endless belt and rotates at the same speed as the paper web. In order to achieve a frictionless dewatering process, it is important that the rotating belt is loaded within certain tolerances with a given tensile stress. This is achieved by regulating the belt traction, in which instance one of the rollers is designed as a force measuring roller for determining the belt traction and one roller is designed as a tension regulating roller. The force measuring roller comprises a force sensor on each of the two opposed supports that measures the support force. The tension regulating roller is adjusted by a motor operator [servomotor, adjusting motor] in order to tension the rotating belt more or less. In order to achieve a closed control circuit the force sensors are in an operative connection with the tension regulating roller. In order to be able to determine the belt traction directly from the measured support force the rotating belt is deflected by 180° on the force measuring roller. The force measuring roller is looped in the same manner independently of the position of the actuating drive so that the measured support force directly reflects the belt traction. Due to the great looping of the force measuring roller it is necessary to grasp the belt on the inside and also on the outside. Thus, the side of the rotating belt contacted by the paper is also grasped by rollers so that particles from the paper web can accumulate on these rollers. These particles result in defects in the paper web and are therefore undesired.
The invention has the basic problem of creating a device and a method for regulating the tension of a running web that permits a precise regulation of the belt traction with a slight looping around the force measuring roller.
This problem is solved in accordance with the invention with the features of the present invention, as set forth in detail below.